Complex renal cystic masses: current standards and controversies

Bosniak classification system is the only preoperative diagnostic tool that has proven its efficiency in the management of complex renal cystic masses. However, it is reader dependent, despite its clear definition of each category. The overall incidence of malignancy in each category did not change significantly over the past 20 years. Current limitations are interobserver variability among readers and a fact that a significant proportion of Bosniak III masses have benign character. The goal is to depict these masses preoperatively and spare the patients of unnecessary surgeries, which raises the question: What particular findings will help in differentiating a Bosniak IIF lesion from a Bosniak III lesion? Do we need to define critical variables that could improve accuracy of Bosniak classification by developing a future nomogram or risk calculator? Some radiologists and urologists erroneously tend to group Bosniak II and IIF in one category and observe them regularly. It seems that radiographic growth itself is insufficient factor for intervention. The change of internal architecture and presence of enhancement play the most important role in depicting malignant lesions during the time frame of active surveillance.